As means for detecting the position and speed of a movable body, known position/speed detecting apparatuses for detecting the position/speed of a movable body have been available. These devices have a reflection mirror on a stage and use means for calculating a stage position on the basis of the angle of reflection of light output from a light source. An exemplary apparatus is described in Patent Document 1 mentioned below. A laser beam is output from a light source fixed to a position such that a laser beam can be output parallel to the direction in which a movable body moves, and the laser beam is reflected off a reflection mirror disposed on the movable body. The reflected light is allowed to pass through or re-reflected off a half-mirror placed between the light source and the reflection mirror, and this transmissive or reflected light enters a light-receiving element, which measures the amount of the transmissive or reflected light. On the basis of the amount of light, the position and speed of the movable body are calculated.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-126720